The present invention relates to the selection of a line from within an image for purposes of composing a distance or range representing image. The invention in particular relates to the selection of particular lines from such an image having been acquired under utilization of a triangulating measurement principle.
Generally speaking a range image depicts an object, not in a manner in which the individual image points represent brightness value of reflection or emission and/or of the object, but an image point represents a distance value between the object point and a reference point such as is given by the measuring equipment. Methods are known for two dimensional measuring range and distance information so as to establish a range image (see for example P. Levi in Electronik 12, 1983). These known methods can basically be divided into two groups which differ in the process of acquisition data i.e. on the basis of the physics underlying the measurement principles. In one method one uses transit time of electromagnetic or acoustic waves; the other method is based on triangulation. The first mentioned principle is suitable for measuring ranges from infinity down to about 1 meter distance and the accuracy depending on the frequency employed, can be as good as 1 mm. The second principle is for reasons of accuracy limited to short distances of about 1 m and less.
The system and methods using transit time measurement are disadvantaged by the fact that generally the distance ascertained extends between the sensor and the particular point being measured. In one produces for example a complete image through beam deflection for example by means of a rotating or oscillating mirror one obtains a rather elaborate system and the components both the mechanical and the optical ones are quite expensive. Triangulation permits simultaneous acquisition over an entire line for the range image to be produced. Herein a thin light strip is suitably projected upon an object and observed by a videocamera or the like whereby the viewing axis of the camera and the direction of illumination have a nonzero angle between them. This angle is the basis for a triangulation method and is shown in principle in FIG. 1; the image produced by the camera is for example shown in FIG. 2. One can see the location of the light strip in real space as well as the corresponding image lines which are at that point not range image lines but "real" ones, they are offset to some extent at a magnitude which corresponds to the difference between object and background as far as distance from the acquiring equipment is concerned. The range image is then composed from this information. The known practice of this method is disadvantaged by the fact that the selection time and the assembly time for a complete range image, assuming CCIR video standards and assuming further 50 fields per second, one requires a 5 second assembly time for 256 range image lines.